1. Field of the Invention
This invention relates to a tracer control system which automatically controls the position of start of deceleration control which takes place immediately before a stylus of a tracer head moves into contact with a model.
2. Description of the Prior Art
In one-way profiling, a tracer head is returned by a quick feed operation from a terminate point to a profiling start point in order to shorten the working time. At the profiling start point the tracer head is subjected to deceleration control immediately before its stylus contacts a model to prevent the tracer head from being damaged and a tool from cutting into a workpiece. FIG. 1 explains the path of movement of the tracer head in this tracer control. The profiling start point is detected by a limit switch LSc and the profiling terminate point is detected by a limit switch LSa and a period A is a profiling period. When limit switch LSa detects that the tracer head has reached the profiling terminate point, a quick feed operation is accomplished in such a direction that the tracer head moves away from the model. When limit switch LSb detects that the tracer head has been raised to its uppermost position, a feed axis is changed over to effect a quick feed of the tracer head to the side of the profiling start point. When limit switch LSc detects that the tracer head has returned to the profiling start point, the feed axis switching is accomplished to quickly feed the tracer head towards the model.
On the path of this approach, a limit switch LSd is provided and, upon actuation of the limit switch LSd, deceleration control is effected to switch the quick feed operation to an ordinary approach operation. Then, when the stylus of the tracer head contacts the model, a pick feed is performed by a detection signal from the tracer head and, after a predetermined amount of pick feed is effected, the feed axis is switched to start tracing of the model with the tracer head. Accordingly, reference characters B, C and D indicate quick feed periods, E a deceleration period and F a pick feed period.
The above-mentioned limit switches LSa through LSd are fixedly disposed in advance with respect to the configuration of the model; in particular, the limit switch LSd is positioned in relation to the deceleration characteristic so that the stylus is brought into contact with the model at a predetermined feed speed.
In such conventional tracer control, when the shape of a model MDL is inclined in the pick feed direction as shown in FIG. 2, since the deceleration control is accomplished upon actuation of the limit switch LSd, the deceleration period E gradually increases, as indicated by E'. In other words, the deceleration period becomes unnecessarily long and affects the working time.